Lanolin and certain lanolin derivatives, as examples of lipid materials, are well known for their unique blend of emollient, moisture retentive and skin penetrating properties, particularly in compositions such as cosmetics and medicaments for treatment of the skin and other parts of the body. The chemical constitution of lanolin and its useful properties are discussed for example in European Patent Application EP-A-0602961. Examples of lanolin-containing compositions in the form of oil-in-water emulsions for cosmetic and other applications are disclosed for instance in GB-A-1530064 and U.S. Pat. No. 3,666,857.
Lanolin has also been used historically as a secondary emulsifier in cosmetic products, imparting an improved skin feel to both vegetable oil and petrolatum based systems. However, because of limitations caused by the drag tackiness and odour of unmodified lanolin on its own, its full range of moisturising and other properties has hitherto been little exploited.
In an article by Clark, E.W., Manufacturing Chemist, 1990, 61, 18-23, it is disclosed that lanolin penetrates into mammalian stratum corneum and also emulsifies water at the lanolin/water interface to give a localised water-in-oil emulsion exhibiting a very small droplet size of less than about 6 .mu.m. Thus, the moisturising effects of lanolin within the stratum corneum may be in part due to this ability to form a spontaneous microemulsion. Further evidence of this effect is disclosed in a later article by Clark, E.W., and Steel, I, J. Soc. Cosmet. Chem., 1993, 44, 181-195.
The scientific literature contains several other reports concerning the ability of lanolin, or modified derivatives of lanolin, either alone or in combination with film-forming agents, to act as enhancers of drug release from matrices. Relevant references in this regard include: R. I Ellin, P.J. Levine and D.E. Leco, J. Am. Pharm. Assoc. 1955, 16, 747-749, L. von Sallman, A.E. Grosso, and M.G Marsh, Arch. Opthalmol., 1946, 36, 284-292 and F. Bottari, 20 G. Di Colo, E. Nannipieri, M.F Saettone and M.F. Serafini, J. Pharm. Sci., 1974, 63, 1779-1783.
In the broader field of micellar dispersion technology, it is well known and well documented that stable compositions having useful carrier and penetration properties can be prepared based on the formation of so-called liposomes, which can approximately be defined as aqueous dispersions of particles which are themselves made up of one or several concentric lipid bilayers within which other molecules can be incorporated. GB-A-1539625 and GB-A-2013609 for example disclose stabilised liposome-based dispersions, in which the liposomal spherules are capable of encapsulating various active substances. Various ionic or nonionic lipid compounds are disclosed, the preferred being a nonionic lipid compound selected from certain linear or branched polyglycerol ethers, polyoxyethyleneated fatty alcohols, various polyol esters or natural or synthetic glycolipids.
EP-A-0585157 and published International patent application WO 87/06499 both disclose the formation of liposome-like particles which incorporate long chain alcohols, some of which are known to be provided by lanolin alcohols, and which are stabilised by the necessary presence of cholesterol or cholesterol sulphate salts. However, we have discovered that the stabilising effect claimed for cholesterol and its sulphate salts is not an essential requirement and that simple microemulsions or liposome-like structures exhibiting excellent physical stability can be produced using lanolin-based materials with a particularly small particle size, the compositions produced being low in viscosity and not necessitating the inclusion of stabilisers or auxiliary emulsifiers.